Defeating Emporor Sun Li
Use the opposite of his style. For example, if he uses his blade use martial styles. If he uses martial styles use your weapon or just kill him using the Jade Golem Spirit.

Recommended character build
Select Tiger Shen (Strong) as your character. Choose his default Martial Style, White Demon (fully upgrade it whenever you have a chance, except for the Chi Damage, as it is not that useful. When you choose your first weapon, get the sword Fortune's Favorite. Do not spend any points in it. Keep gathering enough money to buy the Leaping Tiger Martial Style. Fully upgrade it as well, except for the Chi Damage. If you are playing in the Way of the Open Palm, help Master Radiant at the quest "The Black Leopard School" and kill Smilling Hawk to receive the Paralyzing Palm Support Style. If you are playing in the Way of the Closed Fist, get some money to buy the Storm Dragon Support Style. If neither of the two, full upgrade the one you selected, except for Chi Damage. In the Scholar's Garden at the Imperial City, finish the quest "The Outlander", defeat Sir Roderick, and choose his weapon, Mirabelle, as your reward. Do not upgrade her yet. In the Arena at the Imperial City, at the quest "The Imperial Arena", let Black Whirlwind fight against Kai Lan the Serpent, to receive the Tang's Vengeance, a pair of Dual Wield Axes (full upgrade it). After upgrading all the other Martial and Support Styles and your Weapon Tang's Vengeance, put all your points in Mirabelle. Always have Dawn Star or Sik Fox with you as Support: Dawn recovers you Chi, while Silk enhances your Weapon. Tang's Vengeance drains your Focus, so you do not have to worry about it. After doing all this, your character will be very powerful. Use the Storm Dragon or Paralyzing Palm to stop your enemies (if they are humans or ghosts), and beat them with the Tang's Vengeance against humans and the White Demon (use the Leaping Tiger if the enemy is too fast for White Demon) against ghosts. Mirabelle and Tang's Vengeance are great to defeat Demons with. Mirabelle is exceptional against Horse Demons because they explode after you kill them. Chi Damage is not that good as it seems. It sucks your Chi, and the additional damage is not worth the cost. Also, you need to save Chi in case you are damaged. Perhaps the only battle that will be more though is the one against the two Lotus Assassins and the two Jade Golems.